A、Two. B、Twenty-six. C、Twenty-eight. D、Thirty. C原文中说鹦鹉原来的词汇量是28个，“a twenty - eight vocabulary”。

For centuries, parrots have been prized pets because of their strange talent for imitating human speech. They are able to hear vocal ranges, memorize the tones, and then repeat what they have heard. Often this skill is used to entertain people. But recently, an Amazon parrot, named Baby, was able to put this ability to work by helping police break up a gang of burglars responsible for over $ 50,000 in property theft.
    Baby helped the police to identify the gang of thieves. A recent robbery victim reported to the Baytown, Texas police that her parrot, Baby started acting strangely and saying new phrases after the robbery.  Before the robbery, Baby had only a twenty - eight vocabulary; afterwards, the bird started saying the additional phrases "Come back, Robert !" and "Come here, Ronnie !"
    The police detectives were delighted. Although one man had already been arrested, Ronnie and Robert were the names of their two top suspects who were believed to have aided the first man. Under questioning, this suspect explained what had happened. When the robbers entered the house, they heard Baby talking and thought that someone was home. Ronnie and Robert began running away, while the third man yelled for them to come back. Baby remembered this incident and recorded their voices in her memory.